If I have a number of garden beds, separated by lawn etc, will the worms spread out underground to benefit beds other than the one I have put my Subpod in?
This is unlikely as the composting worms live in the uppermost layers of leaf litter decomposing on the soil surface, so unless you covered the lawn with a mulch layer, the composting worms would not travel the lawn between beds. There is an easier remedy which is to scoop the castings from your Subpod and add them directly around the plants in your other garden beds ;-)